1. Field of the Invention
The present invention relates to fail-over storage systems employed for computer systems. More particularly, the present invention relates to fail-over storage systems provided with a plurality of input/output interfaces.
2. Background of the Invention
Interfaces (I/F) used between storage systems and computers are roughly classified into two types. The first type is the “block I/O interface.” This interface enables data input/output (I/O) in blocks, a block being a unit of data management of storage units. The fiber channel, the SCSI (Small Computer Systems Interface), the Mainframe channel, etc., belong to this “block I/O interface” type. Multiple computers are often connected to multiple storage systems by such block I/O interfaces in systems. The systems are referred to as a storage area network (SAN). Fiber channels are usually used to interconnect a SAN.
The second type of interface is the “file I/O interface.” This type of interface enables data I/O in files. Interfaces that enable data I/O by using the Network File System, a protocol used to transfer files between file servers and client servers, are file I/O interfaces. A storage system provided with this type of file I/O interface and capable of connecting a network, including a local area network (LAN), is referred to as a network attached storage (NAS) system.
A conventional technique, disclosed in U.S. Pat. No. 5,696,895, referred to as the fail-over technique assures the resistance of file servers to failures. Specifically, the technique enables “heartbeat” signals to be exchanged between a first server that uses a first storage system and a second server that uses a second storage system. If a failure occurs in the first server, the “heartbeat” signal stops. The second server detects the absence of signal and accesses the first storage system used by the first server to take over the processing of the first server (fail-over processing).